I wanted to find a reflector holder to use outside that was portable and relatively light, but wouldn't blow around in the wind. This is my prototype.
I took an old real estate sign holder which stakes into the ground and bolted a 24x28" piece of reflective material to it, using galvanized duct tape on the front side, so the bolts didn't pull through.
It goes into the ground easily and doesn't seem to blow around much, despite it being windy today. My main concern at this point is that it's only 48" tall, so if the subject is standing, the light may be a little low.